您錯過了類路徑中的mysql-connector-j jar文件。使用“ java -cp。：MysqL.jar …”。哦這是一個webapp！然后把MysqL jar文件放到WEB-INF / lib文件夾中。

因此，我有一個用于MySQL JDBC驅動程序的.jar文件，該文件位于我的庫源文件夾下，并且具有以下代碼：

public static Connection getConnection() throws SQLException {Connection conn = null;try{ Class.forName('com.mysql.jdbc.Driver').newInstance(); String url = 'jdbc:mysql://50.56.81.42:3306/GUEST_BOOK'; String user = 'user'; String password = 'pass'; conn = (Connection) DriverManager.getConnection(url,user,password);}catch(ClassNotFoundException e){ e.printStackTrace();}catch(InstantiationException e){ e.printStackTrace();}catch(IllegalAccessException e){ e.printStackTrace();} return conn; }

但是，它總是給我這個錯誤：

INFO: Server startup in 645 msjava.lang.ClassNotFoundException: com.mysql.jdbc.Driver at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1678) at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1523) at java.lang.Class.forName0(Native Method) at java.lang.Class.forName(Class.java:169) at gbook.DbHelper.getConnection(DbHelper.java:14) at gbook.DbHelper.getGuestBook(DbHelper.java:51) at org.apache.jsp.index_jsp._jspService(index_jsp.java:83) at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70) at javax.servlet.http.HttpServlet.service(HttpServlet.java:722) at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:433) at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:389) at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:333) at javax.servlet.http.HttpServlet.service(HttpServlet.java:722) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:304) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210) at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:224) at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:169) at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:472) at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:168) at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:100) at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:929) at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118) at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:405) at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:964) at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:515) at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:302) at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908) at java.lang.Thread.run(Thread.java:680)Dec 1,2011 1:41:05 PM org.apache.catalina.core.StandardWrapperValve invokeSEVERE: Servlet.service() for servlet [jsp] in context with path [/JDBC-MySQL] threw exception [javax.servlet.ServletException: java.lang.NoClassDefFoundError: com/mysql/jdbc/Connection] with root causejava.lang.ClassNotFoundException: com.mysql.jdbc.Connection at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1678) at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1523) at gbook.DbHelper.getGuestBook(DbHelper.java:52) at org.apache.jsp.index_jsp._jspService(index_jsp.java:83) at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70) at javax.servlet.http.HttpServlet.service(HttpServlet.java:722)

這是我添加jar文件的方法。我創建了一個lib文件夾，并將jar放入其中，然后在eclipse中配置構建路徑，并將lib文件夾中的jar添加到了項目中。